Built in 1854, Old St. Pat's survived the Great Chicago Fire to become the oldest standing church in Chicago. If you've only been to attend the annual "World's Largest Block Party," check out the Celtic-inspired interior. 700 W. Adams St.; Saturday closed, Sunday 1 to 4:30 p.m.

Built in 1854, Old St. Pat's survived the Great Chicago Fire to become the oldest standing church in Chicago. If you've only been to attend the annual "World's Largest Block Party," check out the Celtic-inspired interior. 700 W. Adams St.; Saturday closed, Sunday 1 to 4:30 p.m.

The Chicago Architecture Foundation’s Open House Chicago is a two-day, behind-the-scenes tour of the city’s architectural structures: some well-known, some regular tourist stops, and some only open to the public for Open House. We recommend you make out a schedule, but don’t get too disappointed if you don’t make it to all the buildings on your list. (Five tours in one day was all we could do at last year’s Open House before we got tuckered out!)